Ok, but I somehow feel that I should build a FX lens system, which makes migration later easier if required, reduces the risk of the DX system being eaten away by the cheaper micro four thirds and cheaper FX cameras (D600 as it is rumoured to be), no one would also want to buy it even 2nd hand.

I'd advise against it. Unless you know exactly what you are looking for, the extra bit of quality that you are looking for by mounting FX lenses on DX will be illusive. If you can't describe precisely now how your 16-85 isn't meeting your expectations, you won't know what to look for by shooting with a more expensive set of lenses. The opportunity cost is that you would be carry around a set of somewhat awkward focal lengths, and your budget will be effective slashed because of the extra cost per lens.

Have a look at some of the DX ultrawide zooms in the 10-24, 11-16 range before committing to something. I think you'll find that you can get extra utility at a lower price.